Monthly gases concentrations of SO2, HNO3, NH3, NO2 and O3 are measured using passive sampling techniques. The INDAAF passive samplers were developed at the Laboratoire d’Aérologie according to the WMO (WMO GAW report n°829) procedures and based on the work of Martin Ferm [1991, 1994]. They have been tested and validated at the INDAAF stations [Al Ourabi and Lacaux, 1999; Lacaux, 1999] as well as in other tropical and subtropical regions [Ferm and Rodhe, 1997; World Meteorological Organization (WMO), 1997; Carmichael et al., 1996]. The validation method, the reproducibility and the detection limits of INDAAF passive samplers are given in Adon et al. (2010).

Collection procedure

Samplers are installed at all stations, mesh-side down, on the underside of a stainless steel support to avoid direct impact from wind and splashing from precipitation. The support is attached to a pole at a height ranged between 1.5 and 3 m. The samplers are exposed for one month, until collection and replacement. All samplers are exposed in pairs so as to ensure reproducibility of results and to reduce data loss if a particular sampler suffers interference.

The figure below presents the typical design of an IDAF passive sampler.

Figure: Diagram of the IDAF passive diffusion sampler